Viruses inhibit TIR gcADPR signalling to overcome bacterial defence

Abstract

The Toll/interleukin-1 receptor (TIR) domain is a key component of immune receptors that identify pathogen invasion in bacteria, plants, and animals. In the bacterial antiphage system Thoeris, as well as in plants, recognition of infection stimulates TIR domains to produce an immune signaling molecule whose molecular structure remained elusive. This molecule binds and activates the Thoeris immune effector, which then executes the immune function. We identified a large family of phage-encoded proteins, denoted here Thoeris anti-defense 1 (Tad1), that inhibit Thoeris immunity. We found that Tad1 proteins are "sponges" that bind and sequester the immune signaling molecule produced by TIR-domain proteins, thus decoupling phage sensing from immune effector activation and rendering Thoeris inactive. A high-resolution crystal structure of Tad1 bound to the signaling molecule revealed that its chemical structure is 1′-2′ glycocyclic ADPR (gcADPR), a unique molecule not previously described in other biological systems. Our results define the chemical structure of a central immune signaling molecule, and reveal a new mode of action by which pathogens can suppress host immunity.

Plant and prokaryotic TIR domains generate distinct cyclic ADPR NADase products

“…Plant and prokaryotic TIRs use enzymatic activities to produce immune signals in response to pathogen challenges (Ofir et al, 2021; Eastman et al, 2022a; Essuman et al, 2022; Lapin et al, 2022). Deciphering the unique structures and physiological outputs of TIR-signals is progressing, but remains challenging (Wan et al, 2019; Duxbury et al, 2020; Essuman et al, 2022; Huang et al, 2022; Jia et al, 2022; Leavitt et al, 2022). In this report, we generated an auto-active variant of the prokaryotic TIR, ThoerisB (ThsB) and reconstructed Thoeris inputs and outputs in planta , to test the hypothesis that plant and prokaryotic signals are conserved.…”

“…During the preparation of this manuscript, two independent studies on the Thoeris system were posted to Biorxiv by Leavitt et al and Manik et al, respectively (Leavitt et al, 2022; Manik et al, 2022). In contrast to Manik et al and the report here, Leavitt et al identifies 2’cADPR as the Thoeris activation signal (Leavitt et al, 2022). Leavitt also identified a phage-encoded repressor of Thoeris, Tad1 (Thoeris anti-defense 1), which blocks ThsA-activation by sequestering cADPR-isomers.…”

“…ThsA orthologs have varying sensitivity to different TIR-derived products (Manik et al, 2022). ThsA-activation by particular cADPR-isomers might also be under selection in response to Tad1-containing phages (Leavitt et al, 2022). It will be interesting to assess ThsA-stimulation by the unknown cADPR-isomer produced by ThsB-Auto, and if Tad1 similarly blocks this putative signal as well.…”

“…It is possible that this unstimulated ‘background’ NADase activity of ThsA in vitro is influenced by recombinant protein preparation. Whether Thoeris systems impose host fitness penalties is not clear (Bernheim and Sorek, 2020); however, because ThsA can be readily expressed in E. coli , it presumably is not strongly cytotoxic to host cells (Ka et al, 2020; Ofir et al, 2021; Leavitt et al, 2022; Manik et al, 2022). Further studies could examine whether the SLOG-domain, in absence of ThsB-signals, is influenced by other cellular metabolites or regulators which act to repress unstimulated ThsA NADase activities.…”

“…While v-cADPR (2’cADPR) is a biomarker of plant TIR-pathway activation by pathogens, a later study reported that v-cADPR-generation by a prokaryotic TIR, AbTir (from human pathogen Acinetobacter baumanii ), was insufficient to stimulate EDS1- mediated plant hypersensitive (HR) cell death (Duxbury et al, 2020). Potential conservation among plant and prokaryotic TIR-immune signals remains unclear (Ofir et al, 2021; Leavitt et al, 2022). Here, we examined whether the NADase-derived signals from the Thoeris immune TIR, ThsB, are functionally compatible with plant TIR-pathways.…”